Electronic circuitry provides complex functionality that is proving ever more useful. One type of circuit is a sensor that senses a physical parameter to be measured (such as, for example, pressure), and generates an electrical output signal that represents the measured parameter.
However, the electrical signal output from the sensors may vary with temperature even given a constant value of the physical parameter being measured. More specifically, temperature variations may cause the offset and gain of the electrical signal output from the sensor to vary thereby introducing temperature-induced inaccuracies into the measurement.
Accordingly, sensor circuits often include a signal path that follows the sensor and that allows for some calibration of the circuit to at least partially compensate for these temperature variations. FIG. 5 illustrates an example configuration 500 of a sensor 501 followed by a signal processing path 510. In this model of a signal processing path, the calibration of the sensor is accomplished by adjusting four parameters of the signal processing path to adjust for the temperature variations of the sensor. These four parameters of the signal processing path include 1) offset (Offset), 2) offset temperature coefficient (OTC), 3) gain (Gain), and 4) gain temperature coefficient (GTC) of the signal path. These values may be provided from the illustrated registers 550, and may be set during calibration through the use of a serial communication interface 560. A Proportional To Absolute Temperature (PTAT) circuit 541 generates an analog representation of the absolute temperature of the circuit. The analog representation of temperature is then converted into a digital temperature representation (Tcode in the case of FIG. 5) using Analog to Digital Converter (ADC) 542.
The signal processing path can be described by the following Equation 1:Vout=(Vin+Offset+OTC*Temp)*(Gain*[Kg+GTC*Temp])   (1)where                Vout is the output of the signal path;        Vin is the output of the sensor coming into the signal path;        Offset is the offset at a reference temperature;        Gain is the gain at a reference temperature;        Temp is the difference between the actual temperature and the reference temperature and is a function of Tcode;        OTC is the offset temperature coefficient;        GTC is the gain temperature coefficient; and        Kg is the gain of the amplifier.        
During calibration, the (OTC*Temp) term and the (GTC*Temp) term confound the Offset and Gain terms. For some forms of conventional calibration, the Offset and Gain terms are set at one value of Temp. Then the OTC and GTC terms are set at another value of Temp, thereby causing the Offset and Gain terms to lose calibration at the first value of Temp. To get accuracy, the calibration would involve cycling between the two temperatures, fine tuning the calibration iteratively to get the calibration accurate across both temperatures. This involves actually exposing the circuit iteratively to different temperatures, which can require significant calibration time and expense.